FIG. 1 depicts a schematic diagram of local area network 100 in the prior art, which comprises point coordinator 101; telecommunication stations 102-1 through 102-K, wherein K is a positive integer; and shared-communications channel 103, interconnected as shown. Stations 102-1 through 102-K enable associated host computers to communicate. Point coordinator 101, a specialized station, enables stations 102-1 through 102-K to communicate with each other.
Each station in local area network 100 is able to transmit into shared-communications channel 103 a block of data called a “frame” to another station. To transmit the frame, the station has to follow a standard procedure to gain access to shared-communications channel 103. A centralized polling protocol is one such procedure.
In a centralized polling protocol, point coordinator 101 sends polls to stations 102-1 through 102-K, granting them opportunities to transmit. Each polled station may transmit its buffered frames, each frame being acknowledged by point coordinator 101. If point coordinator 101 has buffered frames destined for a polled station, station 102-3 as an example, point coordinator 101 may transmit these frames together with the poll. Since each station transmits only upon receiving a poll, transmission is contention-free.
To improve the efficiency of frame exchange, according to the protocol, a transmitting station may combine in the same frame i) acknowledgements to a received frame and ii) data transfers. This is called “piggybacking.” Similarly, point coordinator 101 may also “piggyback” acknowledgements and data transfers, as well as polls, in the same frame. For example, during a frame exchange with point coordinator 101, station 102-3 may piggyback an acknowledgement with a data transfer in the same frame if point coordinator 101 had previously transmitted a frame comprising data to station 102-3. (The acknowledgement is necessary because the previously transmitted frame comprising data requires an acknowledgement.)
Polling protocols require that frames be exchanged within a specified time interval. If the recipient does not acknowledge transmission within the time interval, the source will repeat the transmission. The problem is that the requirement can become difficult to meet if the response frame necessitates computationally intensive processing before transmission. For example, if the acknowledgement is to be piggybacked with a poll or data or both, the time required to generate the combined frame and encrypt it might be longer than the specified time interval.
What is needed is a technique that deals with polled data exchanges between stations without some of the costs and disadvantages of doing so in the prior art.